1. Field of the Invention
The present invention relates to an object detection apparatus which is used to detect a specific object such as a face in an input image.
2. Description of the Related Art
Conventionally, examples of a method of detecting the specific object such as the face from the input image include a method of applying template matching to reduced images which are hierarchically produced to the input image (PP. 203, Digital Image Processing, CG-ARTS Society) and a method of converting the input image into an image called integral image to integrate a weight corresponding to a size of rectangular feature amount (U.S. Patent Application No. 2002/0102024 A1). A method of narrowing down object candidates of the hierarchical image with motion information or color information is proposed as a method of reducing a processing time (see Japanese Patent Laid-Open No. 2000-134638).
In the conventional techniques, a determination whether or not the specific object exists in a determination region is made while the determination region is slightly moved on the input image. In the method of applying the template matching, a correlation and a differential sum of squares are frequently used in the matching, and it takes a long time to perform the computation. In the method in which the integral image is used, it has been confirmed that the method is operated at relatively high speed on a personal computer. However, a large memory resource is required to perform the conversion into the integral image and the computation of the rectangular feature amount, and a large load also applied to CPU. Therefore, the method in which the integral image is used is not suitable to implementation on a device.
The method of narrowing down the object candidates with the motion information or color information is hardly applied when the specific object is not moved. Additionally, because the color information heavily depends on the light source color and the like, it is difficult to make the stable detection.